1. Field of the Invention
The present invention relates to a method for fabricating Surface Acoustic Wave filter packages and a package sheet used therein, and more particularly, to a method for fabricating Surface Acoustic Wave (hereinafter will be referred to as ‘SAW’) filter packages using a package sheet having an outline pattern and anti-bur holes and a package sheet used therein.
2. Description of the Related Art
SAW filters are key parts for processing frequency signals in various frequency bands up to GHz bands. In particular, the SAW filters are more widely used for RF mobile communication based upon their excellent characteristics such as mass productivity, selectivity and stability.
The SAW filters are gradually getting reduced in their sizes. Accordingly, recently a Chip Size Package type SAW filter is produced. (Hereinafter Chip Size Package will be referred to as ‘CSP’.)
In a CSP, as shown in FIG. 1, an SAW filter chip 10 is placed on a package sheet 13, electrically connected via bumps 14. The SAW filter chip 10 attached to the package sheet 13 has a protective layer 11 formed of a resin and a metal shield 12 covered on the protective layer 11.
FIGS. 2a through 2f illustrate a conventional process for fabricating CSP SAW filter packages.
As shown in FIG. 2a, a plurality of SAW filter chips 10 are prepared together with a package sheet or substrate 13, and bumps 14 are provided on undersides of the SAW filter chips 10 for mounting the SAW filter chips 10 on the substrate 13.
The SAW filter chips 10 are attached on the substrate. The SAW filter chips 10 are spaced from one another at a predetermined distance so that the SAW filter chips 10 can be separated into respective packages (FIG. 2b).
A protective layer 11 made of a resin is covered on and filled between the chips 10 on the substrate 13. Examples of the resin may include a thermosetting resin or a photosensitive film. The protective layer 11 allows the SAW filter chips 10 to be in contact with the underlying substrate 13, and also functions to maintain air layers under the SAW filter chips 10 (FIG. 2c).
The protective layer 11 is removed, for example, grooved from predetermined regions of the substrate 13 along which the sheet 13 will be cut into respective packages. This grooving procedure can be performed through a mechanical process to dig the predetermined regions of the substrate 13 to a predetermined depth. Alternatively, a photo-processing such as exposure can be used to remove predetermined regions of the photosensitive resin (FIG. 2d).
Upon completion of the grooving, a metal shield 12 is formed on outer contours of the SAW filter chips 10. The metal shield 12 is formed in the form of at least two metal shield layers through plating in order to screen external noises as well as promote reliability against external environment (FIG. 2e).
The substrate is diced in order to separate the SAW filter chips 10 covered with the metal shield 12 into the respective packages (FIG. 2f).
In the conventional process for fabricating SAW filter packages, the metal shield layer is formed on outer faces of the SAW filter chips and outer face portions of the package sheet. The shield layer is made of metal, whereas the SAW filters and the substrate are made of non-metal. In particular, because the substrate is made of ceramic, the bonding force maintaining these two materials adhered together is lowered. As a result, the shield layer may be separated or delaminated from the substrate during a package-cutting process thereby heavily degrading the reliability of a product. Such delamination is shown in FIG. 3a, in which the metal shield 12 is separated from the substrate 13.
Further, the substrate is grooved to expose the terminals of the substrate for the purpose of grounding the SAW package through the shield layer. However, if the chip is not correctly aligned with the pattern of the substrate, the SAW package is not grounded, thereby lowering the quality and reliability of the product.
Moreover, since the shield layer of the SAW package contains very soft Cu as its main component, the problem of burs, that is, metal fragments from metal shield during dicing can be caused. The burs are mainly produced at corners of the package as shown in FIG. 3b. The burs are produced in lateral and longitudinal cutting processes and may cause severe problem in mounting, storage and reliability of package.